1. Field of the Invention
This invention relates to a master information carrier for magnetic transfer carrying thereon an irregularity pattern representing information to be transferred to a magnetic recording medium.
2. Description of the Related Art
With an increase in information quantity, there is a demand for a magnetic recording medium which is high in memory capacity, low in cost and preferably requires a short time to read out a necessary part of data (a magnetic recording medium which allows so-called high-speed access). As an example of such a magnetic recording medium, there has been known a high recording density magnetic medium such as a hard disc, a zip (Iomega) and the like. In such a high recording density magnetic medium, the recording area is formed by narrow data tracks. In order to cause a magnetic head to accurately trace such narrow data tracks and reproduce the data at a high S/N ratio, the so-called servo tracking technique has been employed.
In order to perform the servo tracking, it is necessary to write servo information such as servo tracking signals for positioning the data tracks, address signals for the data tracks and reproduction clock signals on the magnetic recording medium as a preformat upon production thereof. At present, such preformat recording is performed by the use of a specialized servo recording apparatus (a servo track writer) However, the preformat recording by the conventional servo recording apparatus is disadvantageous in that it takes a long time since the servo information must be recorded on the magnetic recording medium one by one by the use of a magnetic head, which deteriorates the productivity.
As a method of recording the preformat accurately and efficiently, there has been proposed, for instance, in Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544 and 10(1998)-269566, a magnetic transfer method in which a pattern which is formed on a master information carrier and represents servo information is copied to a magnetic recording medium (a slave medium) by magnetic transfer.
In the magnetic transfer, the magnetization pattern representing the information carried by a master information carrier is magnetically transferred from the master information carrier to a magnetic recording medium (a slave medium) by applying a transfer magnetic field to the slave medium and the master information carrier in close contact with each other, and accordingly, the information carried by the master information carrier can be statically recorded on the slave medium with the relative position between the master information carrier and the slave medium kept constant. Thus, according to the magnetic transfer, the preformat recording can be performed accurately and the time required for the preformat recording is very short.
We, this applicant, have proposed in Japanese Unexamined Patent Publication No. 2001-14667 a method of magnetic transfer in which the magnetization pattern on a master information carrier is magnetically transferred to the magnetic layer of a slave medium by forming the magnetic layer on the surface of the protruding portions of the master information carrier of soft magnetic material which is small in coercive force, initially DC-magnetizing the magnetic layer of the slave medium in one direction of the recording tracks and applying a transfer magnetic field to the slave medium in the direction opposite to the direction of the initial-DC-magnetization with the magnetic layer of the slave medium held in close contact with the soft magnetic layer of the master information carrier.
In order to improve the transfer quality (the quality of the signal transferred to the slave medium), it is necessary to uniform the space between the master information carrier and the slave medium. Since it is difficult to uniformly space the master information carrier and the slave medium over the entire area of the slave medium, the master information carrier and the slave medium are generally brought into close contact with each other. Also in the case where the master information carrier and the slave medium are brought into close contact with each other, it is important to uniformly brought into close contact with each other over the entire area. That is, when the slave medium is unsatisfactorily brought into close contact with the master information carrier at a part, the intensity of the magnetic field becomes non-uniform in the transfer magnetic field around the part and non-uniformity of magnetization can occur in an area of magnetic transition or in an area of magnetic uniformity. As a result, the quality of the transferred signal deteriorates and in the case where the signal to be transferred is a servo signal, satisfactory tracking function cannot be obtained on the slave medium, which deteriorates the reliability of the slave medium.